Hi Jesper,
Gotcha 😊
For me, I don’t like two versions of lambda expression… it will confuse
developers.
Cheers,
Daniel.Sun
发件人: Jesper Steen Møller [via
Groovy]<mailto:[email protected]>
发送时间: 2017年2月7日 23:44
收件人: Daniel Sun<mailto:[email protected]>
主题: Re: Lambda vs. Closure (was: [VOTE] Apache Groovy Roadmap)
On 7 Feb 2017, at 16.27, Daniel Sun <[hidden
email]</user/SendEmail.jtp?type=node&node=5738482&i=0>> wrote:
To fully support *real* lambda expression, (to be honest)currently I have
no idea how to generate bytecode for it. In addition, supporting Static
Compilation will be another big work…
A real lambda expression is implemented in Java as an invokedynamic call which
makes use of a bootstrap method calling into a class called the
LambdaMetafactory
(https://docs.oracle.com/javase/8/docs/api/java/lang/invoke/LambdaMetafactory.html)
, and puts the body of the lambda expression into a hidden method on the
class. The LambdaMetafactory sets up the magic class which holds any escaped
variables and implements the functional interface. To work, it requires EXACT
type information, so it's only possible to do this in static compilation.
* For instance, we could warn the user if the lambda referred to 'this' or
'super' directly.
I think ‘this’ and ‘super’ can be referred but developers should not change its
resolve strategy, so we can forbidden the scenario by syntax check 😊
I would like to open a new discussion based on our discussion in the
dev-list later and wish others would think same with us to accept the closure
with lambda syntax
I'm not sure why we need a separate discussion.
We have a basic choice: 1) Use Java-lambda semantics or 2) Groovy-closure
semantics. As a variation on 2, we can add some help for people pasting Java
code into a Groovy program.
Generating faster/tighter code for lambdas (or even closures) can be
implemented as a separate task, the two aren't really interconnected, since the
Groovy closure is so versatile to begin with.
-Jesper
发件人: <a href="x-msg://13/user/SendEmail.jtp?type=node&node=5738481&i=0"
target="_top" rel="nofollow" link="external" class="">[hidden email]
发送时间: 2017年2月7日 23:10
收件人: <a href="x-msg://13/user/SendEmail.jtp?type=node&node=5738481&i=1"
target="_top" rel="nofollow" link="external" class="">[hidden email]
主题: Lambda vs. Closure (was: [VOTE] Apache Groovy Roadmap)
(changing the subject so we don't disrupt the main discussion)
Not quite 😔
The changes in Java to support Lambdas are much deeper than just how the
Metafactory is invokedynamic'ed, as it changes how type inference and overload
resolution is done. Same as with the issues we discussed a while back around
method references: Supporting Java8 semantics in the Groovy compiler is a very
big task, as we just don't have the type information available.
I would much rather suggest supporting the lambda syntax with groovy semantics,
but add warnings if we detect that the code may rely on Java lambda semantics.
For instance, we could warn the user if the lambda referred to 'this' or
'super' directly.
-Jesper
On 7 Feb 2017, at 16.00, Daniel Sun <<a
href="x-msg://13/user/SendEmail.jtp?type=node&node=5738478&i=0"
target="_top" rel="nofollow" link="external" class="">[hidden email]> wrote:
Hi Jochen,
That’s great!
Paul and Graeme are both afraid of future breaking changes of groovy’s lambda
expression, which is currently based on closure. If we could generate *real*
lambda bytecode for LambdaExpression, groovy’s lambda expression will behave
same with Java8’s at runtime😊
Cheers,
Daniel.Sun
发件人: <a href="<a
href="x-msg://12/user/SendEmail.jtp?type=node&amp;node=5738477&amp;i=0"
class="">x-msg://12/user/SendEmail.jtp?type=node&node=5738477&i=0"
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发送时间: 2017年2月7日 22:23
收件人: <a href="<a
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主题: Re: [VOTE] Apache Groovy Roadmap
On 07.02.2017 14:44, Daniel Sun wrote:
> Hi Cédric,
>
> It seems that too many choices are a annoying problem, but I
> believe we can conquer it sooner or later ;)
> BTW, is it possible to keep groovy' lambda expression as it
> is(i.e. groovy closure with lambda syntax) but generate *real* lambda
> bytecode for
> it(https://github.com/apache/groovy/blob/parrot/src/main/org/codehaus/groovy/ast/expr/LambdaExpression.java)?
sure, you should make a visitLambdaExpression similar to
visitClosureExpression and change our visitors
bye Jochen
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